1. Field of the Invention
The present invention relates to a charging system for charging a battery and to a battery pack. More specifically, the present invention relates to a charging system for charging a first battery which can be charged at a constant current, such as a nickel-hydrogen battery, and a second battery which cannot be charged at a constant current and can be charged only at a potential below the preset level, such as a lithium ion battery, with the same charging device, and to a battery pack in which the second battery which cannot be charged at a constant current is charged by using a charging device for charging the first battery which can be charged at a constant current, such as a nickel-hydrogen battery.
2. Discussion of the Prior Art
Nickel-hydrogen batteries are presently used as high-performance batteries. Nickel-hydrogen batteries may have a capacity higher than that of nickel-cadmium batteries that have found wide application, but they generate a large amount of heat in charging, and when a high temperature is reached because of such heat generation, the electrodes or separators of the battery inner cell are degraded, shortening the service life and, therefore, making the batteries difficult to handle.
Lithium ion batteries have started finding application as the batteries demonstrating higher performance than the nickel-hydrogen batteries. When a potential above the preset level was applied to the lithium ion batteries, there was even a danger of inflammation and the batteries were very difficult to handle. For this reason, it was necessary to charge the lithium ion batteries at a constant current at the initial stage of charging and to conduct charging at a constant voltage having the prescribed value when the battery voltage reached the preset value so as not to exceed the preset value of the potential.
The inventors have studied the possibility of charging lithium ion batteries with a charging device for charging nickel-hydrogen batteries at a constant current. However, it was predicted that since a potential exceeding the preset value cannot be applied to lithium ion batteries, as was mentioned above, and the lithium ion batteries have to be charged at a constant voltage, a constant-voltage charging circuit has to be added to make the charging possible which will increase the cost.
With the foregoing in view, it is an object of the present invention to provide a charging system which is capable of charging a first battery which can be charged at a constant current, such as a nickel-hydrogen battery, and a second battery which can be charged only at a potential no higher than the preset level, such as a lithium ion battery, with one charging device comprising no constant-voltage charging circuit.
Another object of the present invention is to provide a battery pack suitable for charging a second battery that cannot be charged at a constant current by using a charging device designed for charging a first battery which can be charged at a constant current, such as a nickel-hydrogen battery.
According to the present invention, a charging system for charging a first battery which can be charged at a constant current and a second battery which can be charged only at a potential below the preset level with the same charging device, wherein said first battery comprises a temperature detecting element, said second battery comprises an output unit for outputting a potential corresponding to the battery voltage, and said charging device comprises a detection unit for detecting the temperature of the first battery and the voltage of the second battery, a current value search unit for searching a current value at which the temperature of the first battery that was detected with said detection unit follows the target temperature rise pattern during charging and searching a current at which the voltage of the second battery follows the target voltage rise pattern during charging, and a charging current control unit for charging the batteries at the current value found by said current value search unit.
In the charging system in accordance with the more preferred teaching of the present invention, when the charging device charges the first battery which can be charged at a constant current, such as a nickel-hydrogen battery, charging of the battery is conducted, while the current value is being adjusted so that the temperature follows the target temperature increase pattern. As a result, charging can be conducted within a short time so that the nickel-hydrogen battery demonstrating an intensive increase in temperature is not heated to a high temperature. Moreover, when the same charging device is used for charging the second battery which can be charged only at a potential no higher than the preset level, such as a lithium ion battery, charging is conducted, while the electric current is being adjusted so that the voltage follows the target voltage increase pattern. As a result, the lithium ion battery can be charged at a potential no higher than the preset level. Therefore, the first battery which can be charged at a constant current, such as a nickel-hydrogen battery, and a second battery which can be charged only at a potential no higher than the preset level, such as a lithium ion battery, can be charged with one charging device provided with no constant-voltage charging circuit.
In accordance with the more preferred teaching of the present invention, a detection unit detects the temperature of the first battery based on the potential of a resistor connected to a temperature detecting element incorporated in the first battery. As a result, the detection unit can accurately detect the temperature of the first battery based on the potential of the resistor and also the battery voltage of the second battery based on the potential corresponding to the battery voltage from the output unit of the second battery.
In accordance with the more preferred teaching of the present invention, the first battery stores the temperature rise pattern during charging which is the target for the first battery, and the second battery stores the voltage rise pattern during charging which is the target for the second battery. As a result, various first batteries and various second batteries can be charged according to the respective battery characteristics.
According to the present invention, a battery pack in which the second battery which can be charged only at a potential no higher than the preset level is charged with a charging device conducting charging so that the temperature of the first battery follows the target temperature rise pattern during charging by detecting the temperature of the first battery which can be charged at a constant current by the potential and controlling the charging current so that changes in the potential follow the preset pattern, wherein by outputting the potential corresponding to the voltage of the second battery to said charging device, said charging device is caused to control the charging current so that the changes in the potential follow the preset pattern and to conduct charging so that the voltage of the second battery follows the target voltage rise pattern during charging.
According to the present invention, the battery pack outputs a potential corresponding to the second battery voltage to the charging device. Because of such output, in the charging device, the charging current is controlled so as to obtain the preset pattern of changes in the potential and charging is conducted so that the voltage of the second battery follows the target voltage rise pattern during charging. As a result, the second battery which cannot be charged at a constant current can be charged by using a charging device that can charge the first battery which can be charged at a constant current, such as a nickel-hydrogen battery.